Design and additive manufacturing of thermal metamaterial with high thermal resistance and cooling capability

Metamaterials are defined as artificially designed micro-architectures with unusual physical properties, including optical, electromagnetic, mechanical, and thermal properties. This study proposes a thermal metamaterial that provides an efficient thermal cycle with two conflicting objectives: (i) high thermal resistance as a thermal insulator and (ii) high cooling capability as a heat exchanger. To enable these conflicting objectives, we used cellular lattice structures fabricated by additive manufacturing (AM). An efficient design method based on a finite element (FE) mesh was developed to obtain boundary-conformal lattices for arbitrary 3D shapes. FE analyses were then conducted to evaluate the structural and thermal behaviors of the lattice structures. The designed lattice structures were fabricated by powder-bed fusion (PBF) type AM using Ti-6Al-4V powders. Heat conduction tests were then performed to evaluate the thermal resistance of the lattices with various strut diameters, and the resulting thermal resistance increased five to fifteen times in comparison with that of the pure material. Cooling tests were also conducted to evaluate the cooling capability of the lattices, which showed that the lattice structures could act not only as a thermal insulator but also as a heat exchanger. Consequently, the developed lattice structures can be regarded as a thermal metamaterial that is useful in various applications that require a high thermal cycle of heating and cooling.